That's not really possible on an instant exchange. On "regular' exchanges, the market decides the price. On eXch, it's based on other regular exchanges. It wouldn't dare predict what would happen if eXch were to offer a higher price for Monero than other exchanges. It may lead to all liquidity on those exchanges being eaten by arbitrage traders, more Monero flowing into eXch, and the price spiraling upwards. Either way, I don't think it solves the liquidity problem. But that's just my own speculation of course.
Yeah, but for how long could that be maintained? Who will pay for the higher XMR price?
This is basically an order book, someone has to buy (in this case, exch itself if it doesnt use any third party exchange).
If they raise XMR price for 5%, theoretically they could use all of their other coins reserves to sustain that price for some time... but in the end of the day, when the reserves of other coins are drained, they would not be able to buy the same amount of those coins back